(a) Field of the Invention
The present invention relates to an apparatus for producing electric energy by using salt water and an apparatus for producing fresh water by desalinating salt water.
(b) Description of the Related Art
There are various types of generation apparatus and methods for producing electric energy by using water, and recently, an osmotic power generation scheme using the difference in salinity between seawater and fresh water has been devised.
According to a conventional waterpower generation method (large hydropower generation or small hydropower generation) for producing electric energy by using water, electricity is produced by turning a turbine by using head and a flow rate of water kept in storage in a dam as constructed.
Namely, water is kept in storage at an upper stream of a dam, and the water is discharged to a lower stream of the dam by opening a floodgate such that the water is dropped to thus turn a turbine. In this process, potential energy of water is converted into kinetic energy of the turbine, and a rotor coil within the turbine is turned along the turbine to cause an electromagnetic induction phenomenon to generate current. Through this process, kinetic energy of the turbine is converted into electric energy.
In order to increase the generation capacity in waterpower generation, the discharged water is required to have greater potential energy. Waterpower generation using a dam, however, is disadvantageous in that generation cannot be continued when precipitation is small.
Thus, in order to solve the problem, a pumped-storage power generation, in which water of a lower stream of a dam which has been discharged is pumped up during a time duration in which power consumption is low and then discharged at the time of high power consumption to thus generate electricity, has been devised.
A conventional osmotic power generation scheme includes a process called pressure retarded osmosis (PRO). Namely, it is a scheme of producing power by turning a turbine by using a flow rate increased through osmosis occurring at a membrane and pressure applied in order to retard osmosis by using seawater and fresh water having the difference in salinity.
An output of the turbine is proportional to a head of water and a flow rate, so such a pressure retarded osmosis (PRO) scheme is used. As fresh water moves through the membrane, chemical potential energy of the fresh water is converted into mechanical energy having the same pressure as the pressure applied to seawater. However, this scheme is disadvantageous in that it is available only in an area where seawater (the sea) and fresh water (river) meet.
Meanwhile, a great quantity of water exists on earth, but water people may reliably have is insufficient. For this reason or so, a technique of desalinating seawater has been developed.
In order to obtain fresh water from seawater, a process of removing components inappropriate for water or intake water from components dissolved in or floating on seawater is required.
Methods for desalinating seawater into fresh water includes a reverse osmosis process, an electro-dialysis process, an evaporation process of changing raw water into steam to thus desalinate the water, a freezing process, a solar heat usage method, or the like.
Among the methods for desalinating seawater, the reverse osmosis process and the electro-dialysis process are commonly used.
A desalination apparatus using the reverse osmosis process has a structure in which ionic material dissolved in seawater is removed by a reverse osmotic membrane allowing pure water, excluding an ionic material dissolved in water, to pass therethrough.
In order to separate ionic material and pure water from raw water, a pressure higher than osmosis is required, and the pressure at this time is called reverse osmosis. In case of seawater desalination, a high pressure of about 42 bar to 70 bar is required.
In order to provide such reverse osmosis, the desalination apparatus includes a raw water supply unit (a supply pump, or the like) for pumping raw water.
In general, since the conventional desalination apparatus uses a high pressure pump consuming most power, as a raw water supply unit, it has shortcomings in that a great amount of energy is consumed for desalinating seawater.
A wind-powered desalination apparatus using natural energy without power consumption may also be used. In this case, a raw water supply unit provided in the desalination apparatus has a structure in which raw water supplied by installing a windmill is stored in a pressure tank (a pressurizer) and maintained at a certain pressure, and as high pressure raw water discharged from the pressure tank passes through a preprocessor device, a foreign object is filtered out, and the filtered raw water is put into a reverse osmosis device so that fresh water can be separated by a reverse osmotic membrane.
The windmill employs a structure in which rotary force of a rotor, a blade which rotates by wind velocity, is converted into vertical reciprocal movement to allow a movement member within a cylinder to vertically move to perform pumping.
However, the scheme using a windmill is disadvantageous in that it can be driven only under a condition in which sufficient energy can be obtained through wind velocity. Also, it can be used only under a condition in which salinity is relatively low.
Since the reverse osmosis process consumes much energy, recently, a forward osmosis process of separating water from seawater through only pure osmosis without using a high pressure pump, or the like, has been developed.
However, in the forward osmosis process, a draw solution including a high concentration draw solute compared with seawater is used, it is difficult to separate the draw solute from the draw solution diluted by water moved through a forward osmotic membrane.
Meanwhile, the related art forward osmosis process also has a problem in which a considerably long period of time is required to desalinate seawater.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.